docs: def deserialize_base64(attr):
          """Deserialize base64 encoded string into string.
  
          :param str attr: response string to be deserialized.
          :rtype: bytearray
          :raises: TypeError if string format invalid.
          """
          if isinstance(attr, ET.Element):
              attr = attr.text
          padding = '=' * (3 - (len(attr) + 3) % 4)
          attr = attr + padding
          encoded = attr.replace('-', '+').replace('_', '/')
          return b64decode(encoded)